This application addresses the need to develop a technique for analysis of enamel lesions produced under various demineralizing and remineralizing conditions. These lesions exhibit zones of varying mineral density from the surface to the intact tissue. Our technique of abrasion biopsy will be adapted for the use of bovine enamel slabs following the principles used in an earlier investigation (Weatherell et al, 1985). The subsurface lesions will be produced on 3 x 5 mm enamel surfaces prepared with precise geometrical specifications. Two consecutive acid treatments will be applied. I. Immersion to acid buffers containing various amounts of fluoride (0.1 to 10 ppm). II. Immersion to fluoride-free buffers. Variables of acid concentration, pH, fluoride concentration, and exposure time will be studied for their influence on the development of lesions. The sampling will be conducted by abrasion of the lesion on Lapping Film in increments of 10 Mum measured with a sensitive micrometer. The abraded specimen will be dissolved in HC10 and analyzed for fluoride, phosphorus, and calcium content. On the basis of this data, each sampled layer will be defined in terms of mineral density, calcium to phosphorus ratio, and fluoride content. The abrasion biopsy technique will open possibilities for further studies of the demineralizing and remineralizing conditions "in vitro" and "in vivo" as they influence the development, progression, and possible arrestment of experimental lesions. Such knowledge may lead to a better understanding of the mechanisms of demineralization and remineralization, and possibly suggest better modalities for the clinical treatment of caries.